Influence of temperature and particle size on the single and mixed atmosphere gasification of biomass char with H 2 O and CO 2

Abstract

. Influence of temperature and particle size on the single and mixed atmosphere gasification of biomass char with H2O and CO2. Fuel Processing Technology, Elsevier, 2015, 134, pp.175-188. 10 The paper focuses on the gasification of biomass chars in H 2 O, CO 2 and their mixtures. The first part is dedicated to the study of the influence of particle size and temperature in single atmosphere gasification experiments. The Thiele approach was successfully applied to assess the extent of diffusional limitations. We also studied the mixed atmosphere gasification of 0.2 mm chars at various temperatures and found that the char reactivity is fairly rep resented by an additive law at relatively low temperatures while it is lower than the sum of the individual con tributions for high temperature cases. Similarly, we assessed the effect of particle size for mixed atmosphere experiments and found that an additive law was representative of the experimental reactivities for particle sizes from 0.2 to 13 mm. The present work provides useful and worthy information on the char gasification re activity in conditions close to practical operating ones encountered in biomass gasifiers.

The effects of textural modifications on beech wood-char gasification rate under alternate atmospheres of CO 2 and H 2 O

“…The chars were kept for 1 h at the final temperature, cooled under nitrogen and stored afterwards in a sealed container. The low heating rate is expected to ensure a good temperature uniformity in the wood particle and to lead to a quite homogeneous wood-char, from the structural and chemical viewpoints [2,24,25]. During the pyrolysis reaction, the char particles shrink and get an ovoid form.…”

“…The gas alternation gasification experiments were done at 900°C on the Char02 particles as well as on the Char13. In the former case, there are quite low diffusional limitations while in the second one, the diffusional limitations are quite high [2]. The analysis of the char reactivity curves during gas alternation gasification experiments will help to assess the influence of a gas on the char reactivity towards the second one.…”

“…In this case, there were high diffusion limitations and limited active site concentration available for reaction with H 2 O and CO 2 . The reactivity in mixed atmospheres was consequently lower than the sum of individual reactivities [2]. In a recent study, Roberts and Harris discussed the lack of consensus in the literature in terms of available active surface and total reacting gas partial pressure.…”

“…Inside a gasifier, a biomass particle dries first, then gets pyrolyzed at higher temperature leading to the formation of gasses and a solid char. The pyrolysis gasses as well as the solid char react with the gasification medium (H 2 O, CO 2 , O 2 or mixtures) to produce more Syngas. The char gasification reaction is the limiting step during the gasification process, which makes it worthy of studying and understanding.…”

“…The subject is quite controversial as the conclusions were different from one study to another. A literature overview on this issue is detailed in [2] as well as in [3]. Some authors claimed that H 2 O and CO 2 react independently on the char active sites leading to a char reactivity in a mixed atmosphere which is equal to the sum of the individual reactivities [4][5][6][7][8]:…”